Aggregate all liquidity restrictions in a single place (#1921)

* Clean up session key rotation

* Fix build

* Bump version

* Introduce feature to balances.

* Move staking locking logic over to central point

* ^^^ rest

* First part of assimilation

* More assimilation

* More assimilation

* Fix most tests

* Fix build

* Move Balances to new locking system

* :q!

* Bump runtime version

* Build runtime

* Convenience function

* Test fix.

* Whitespace

* Improve type legibility.

* Fix comment.

* More tests.

* More tests.

* Bump version

* Caps

* Whitespace

* Whitespace

* Remove unneeded function.

substrate/srml/aura/Cargo.toml

@@ -7,7 +7,8 @@ edition = "2018"
 [dependencies]
 hex-literal = "0.1.0"
 parity-codec = { version = "3.1", default-features = false, features = ["derive"] }
-serde = { version = "1.0", default-features = false }
+parity-codec-derive = { version = "3.1", default-features = false }
+serde = { version = "1.0", optional = true }
 inherents = { package = "substrate-inherents", path = "../../core/inherents", default-features = false }
 rstd = { package = "sr-std", path = "../../core/sr-std", default-features = false }
 primitives = { package = "sr-primitives", path = "../../core/sr-primitives", default-features = false }
@@ -27,7 +28,7 @@ consensus = { package = "srml-consensus", path = "../consensus" }
 [features]
 default = ["std"]
 std = [
-	"serde/std",
+	"serde",
 	"parity-codec/std",
 	"rstd/std",
 	"srml-support/std",